Process for the production of printing forms



3,079,358 PROCESS FOR TEE PRQZ'BUCTIQN F PRWTZNG FGRMS Hiidegard Haydn, Gnstav Schaurn, and Edith Weyde,

Leverhusen, Germany, assignors to Agfa Ahtiengeselisehart, Leverhusen, Germany, a corporation oi German No i brawing. Fiied Feb. 5, 1957, Ser. No. 638,199 Claims priority, application Germany Feb. 25, 1956 2 Claims. ((31. 101-129) The present invention relates to a process of producing printing forms and more especially to a process according to which printing forms are produced While making use of the method of heat development of silver halide emulsion layers.

For the production of non-laterally reversed positive copies, it is already known to use the known step of heat development simultaneously with the development of the negative copying original, the developing operation being coupled with a transfer process. With this arrangement, the developing substance which is contained in the photographic silver halide emulsion layers and which has reinained unused at the unexposed areas is transferred to a second layer which is disposed in contact with the first and which contains one or more substances yielding colored compounds with the said developing substance. Oxidiziug agents and aromatic diazo and nitroso compounds are proposed by way of example as reactants in the positive layer.

In the copending application of Hildegard Haydn, Anita von Konig, and Edith Weyde, Serial No. 636,863, filed January 29, 1957, a process is proposed according to which silver halide layers which contain developing substances the oxidation products of which harden gelatine and which can be developed by heat without application of processing baths are brought into contact with a second layer onto which the exposed parts of the emulsion which have remained unhardened are transferred. This transfer of the emulsion parts can take place either during development or subsequent thereto. Thereafter, there is obtained a hardened negative relief and a transferred positive relief which initially is unhardened.

Suitable silver halide developing substances for carrying out this process are polyhydroxy compounds of henzene, naphthalene or diphenyl, which can be substituted in the nucleus by halogen atoms or alkyl, aralkyl, aryl or cycloalkyl groups, for example, pyrocatechol, hydroquinone, 2,3-dihydroxy naphthalene, 2,6 dihydroxynaphthalene, 3,4-dihydroxy diphenyl, 2,3-dihydroxy diphenyl, l,2-dihydroxy-4-cyclohexyl benzene, 4-benzyl pyrocatechol and 4-chloropyrocatechol. With the application of heat, these developing substances not only reduce the exposed silver halide, but they also modify the gelatine, probably due to the formation of oxidation roducts, so that it becomes infusible and unswellable, while it remains unchanged at the unexposed places. This unmodified gelatine of the layer can now be brought, during heat development or at a later stage, into contact with a second layer which has the ability to adhere firmly to the unmodified gelatine so that, when the two layers are separated, parts of the gelatine are stripped from the negative layer. in this way, the non-laterally reversed positive of the copied original is obtained on the second layer, which is the so-called transfer layer, this positive being in the form of a gelatine relief which still contains silver halide and developing substance. If this gelatine relief on the transfer layer is now exposed to diffused light and again subjected to heat treatment, it becomes deep black in color. A black coloring of the positive can also be obtained by using an emulsion of appropriate composition or by adding suitable compounds to the positive layer. It is a particular advantage of the present process that both the development process and transfer process are effected only by heat and Without any additional wet treatment.

Any silver halide emulsion can be used for the production of the negative layer, such a silver chloride, silver bromide, silver chlorobromide, and silver iodobromide emulsions. As binding agent, it is possible to use those which are usual in the photographic art and which are hardened by the action of heat by developer-oxidation products, such as for example, gelatine, polyvinyl alcohol, carboxymethyl cellulose and mixtures of these substances. The pH value of the emulsion is preferably adjusted to about 3.5-6.5. In order to accelerate the initiation of the developing process, it is advisable to add non-tanning silver halide developing substances, such as p-methylamino phenol, p-amino phenol or their substitution products, to the hardening developers in amounts up to about 20% by weight as calculated on the tanning developer.

For stabilising the developing sub-stances, it is possible to add to the photographic layers substances which slowly split off sulphur dioxide or sulphurous acid and the cleavage product of which do not cause either a hardening of the gelatine or any other undesirable influencing of the silver halide emulsion during storage. Examples of such substances are bisulphite compounds of such aldehydes or ketones as do not harden, and aldehydes and ketones which have a relatively high boiling point, particularly a boiling point higher than C. Such aldehydes are aromatic, araliphatic aldehydes, and heterocyclic aldehydes, such as benzaldehyde, terephthalaldehyde, cinnamaldehyde, salicylaldehyde, furfural, whereas cycloaliphatic ketones, such as cyclopentanone and cyclohexanone, and araliphatic ketones, such as benzalacetone, and heterocyclic ketones, such as isatin, are the most sui table ketones. The acetone-bisulphite compound would be less suitable, since this substance only gives slight protection against oxidation of the developer because it has a comparatively strong tendency to decompose with volatilization of the acetone. Examples of substances which are particularly suitable are: terephthalaldehyde bisulphite, cinnamaldehyde bisulphite, benzaldehyde bisulphite, salicylaldehyde bisulphite, cyclohexanone bisulphite, cyclopentanone bisulphite, furfural bisulphite, these compounds being preferably used in the form of their alkali-metal salts, such as sodium, potassium or lithium salts. The organic developing substances are preferably applied in quantities of about 0.5-8 g. per cc. of an ordinary silver halide emulsion, whereas the aforementioned stabilizers are preferably used in quantities of 0.2-2. parts by weight for each part by weight of the organic developing substance.

In addition, it is important that compounds splitting off water should be added to the emulsion of the negative material or the transfer layer. Suitable as such additives are salts of inorganic or organic acids containing water of crystallization, such, as for example, sodium citrate (C H O Na -5H O), calcium acetate trisodium phosphate (Na PO -12H O), sodium sulphate (Na SO EH 0), and/ or substances which ensure a high residual moisture content, such as, for example, glycol, glycerol or sorbitol. These substances are preferably used in such amounts that the water content of the negative material amounts to 8l2, preferably 8-10 percent 'by weight. When these additives are used in the transfer layer, the moisture necessary in the development can migrate during the processing from the transfer layer to the negative layer.

plastics, textile fabrics or metal.

It has now been found that this process can be used very satisfactorily for the production of printing forms which are suitable both for spirit printing and for offset printing.

By spirit printing is understood the process in which an alcohol-soluble dyestuif, after being moistened with alcohol, is transferred as a picture by means of a mechanical device from a printing form to another support, it

being possible in this way for a relatively large number of prints to be produced from the original copy.

For the production of printing forms for spirit printing, two methods can be adopted, according to which either the negative relief or the positive relief is used as the printing form. If it is desired to use the negative as printing form, care must be taken that the unexposed part of the emulsion layer is completely stripped from the support in the processing. After exposure and pro- ..cessing, there is then available an original copy in which only the light areas of the original are covered by hardened emulsion. If the back of the paper support used to carry the hardened emulsion is now brushed with an alcoholic dyestufi solution and the paper to be printed is laid on the front, the dyestuff solution only penetrates the support at the areas at which the silver halide emulsion was removed during the development.

- ,It is obvious that the quality of the support is of importance when this process is, used. It is for example, desirable to use a paper which is comparatively weakly sized or has-a sizing which is permeable to alcohol and thus to dyestuff.

Clean detachment of the negative emulsion is promoted .by an intermediate layer which is disposed between the support and the emulsion layer.

For this intermediate layer preparations are chosen to which the emulsion binding agent adheres less firmly than to the untreated initial .material. For the preparation, there are chosen filmforming high molecular weight compounds which are permeable to alcohol when the negative is used as a printing form for spirit printing, such as zein, ethyl cellulose, polyvinyl acetate and polyethylacrylate. These substances are dissolved in organic solvents such as alcohol and the solution applied to one side of the paper support. The emulsion is then cast thereon in known manner.

If it is desired to use the positive as a printing matrix, there are two different methods which can be adopted.

(1) It is, for example, possible to use a very fine-mesh fabric as support for the positive, the interstices of the said fabric being filled by the emulsion extracted from the negative layer. Such a relief can be treated with a dyestufi solution, such as acid or basic dyestuffs, methylene blue, astra blue or Congo red, which color the binding agent of the emulsion portions. It the printing form treated in this manner is now placed laterally reversed on the material to be printed, which has been briefly coated beforehand with an agent that is capable of dissolving the said dyestuif, the non-laterally reversed dyestuff positive of the original is formed thereon.

(2) The process can, however, also be carried out by transferring the positive dyed with dyestufi? solution to a suitably prepared metal or rubber roller and printing off the positive from this by means of a suitable dyestufi-dissolving agent on to a support. In this way, there is also obtained the non-laterally reversed and positive picture of the original. If it is desired to use the process for offset printing, it is the positive which is initially used, this having been transferred to a metal plate or paper or a plastic foil which is suitable for the offset process, i.e. which does not take up any oil color after moistening.

After processing, a silver image embedded in a binding agent such as gelatine is obtained on these foils. By being subsequently treated with suitable compounds, such as zirconium oxychloride, phospho-tungstic acid or metaphosphoric acid, this image can be caused to absorb O11.

EXAMPLE 1 Negative as Matrix for Spirit Printing ing water of crystallization, 10 g. of. terephthalaldehyde bisulphite and 10 cc. of 5% benztriazole are added to 1 litre of any suitable silver halide emulsion. Other additives such as wetting agents known in the emulsion art can be used.

The emulsion is cast on a paper which has good permeability for alcohol. Care is to be taken that the emulsion does not penetrate into the initial material during the casting, and this is achieved by placing a thin intermediate layer bctween the paper and emulsion layer. ,For this purpose, it is, for example, possible to use a 2% alcoholic solution of ethyl cellulose. The thickness of the emulsion layer should be kept so small, as far as'possible less than 6 microns, that all unhardened gelatine is extracted in a single transfer. The emulsion can also be cast on to a fine-mesh sized or unsized fabric;

it can then be used as a printing form after processing.

The relief forming the positive and lifted from the negative layer is not absolutely necessary in this case. It is therefore possible, for example, to usea polished metal plate as a'support for the positive relief from which the latter is removed after each use. However, if it is desired to use the positive again, one of the indicated transfer layers will be used.

. Processing After exposure, the negative layer is brought into contact with. the transfer layer, for instance a metal. plate. These are both subjected to a temperature of -150 C., preferably to C.,' for 5 to 30 seconds in a press which can be heated. The positive can be heated at a lower temperature. Afterseparation, the g'elatine of the unexposed areas adheres to the transfer layer, for example a metal plate. The negative, on which the emulsion is removed down to the support at the unexposed areas, is coated on the back with the alcoholic dyestufii solution, for example, an alcoholic solution of crystal violet, aniline blue, fuchsine or methyl violet, and the front of the negative is brought into contact with the paper which is to be printed. The dyestuff solution penetrates through the material and is transferred at the stripped areas to the papers to be printed, on which there is formed a non-laterally reversed dyestuflf image of the copied original. The dyestutf solution can also be continuously applied to the back of the matrix by an applicator device, whereby the printed impression is no longer restricted by the amount of dyestuif, but depends only on the durability of the matrix. Thematrix has long durability and can also be used again at a later time.

EXAMPLE 2 Positive as Printing Matrix Negative: 25 grams of 4-cyclohexyl pyrocatechol, dissolved in 30 cc. of dimethyl formamide, 6 g. of cyclohexanone bisulphite, 225 g. of sodium acetate containing water of crystallization and 10 cc. of 5% benztriazole areto 30 seconds at 110-120 C., a positive image is obtained on the fabric after the negative and fabric have been separated. The gelatine has then penetrated into the interstices and has filled them. If such a positive is treated with an aqueous dyestuff solution which is taken up by the binding agent, for example, with an acid or basic dyestufi, such as methylene blue or congo red when gelatine is used, and if it is placed laterally reversed on the material to be printed, a non-laterally reversed dyestuif positive of the original is obtained on the said material. If the material to be printed is moistened with a dyestuff solvent (in the above case water), the printing operation is facilitated. In this case as in Example 1, fresh dyestufi can be applied, either continuously or after a period of time, by an applicator device.

This printing matrix can be kept and can be used again at any time.

EXAMPLE 3 Positive as Printing Matrix Negative: As negative emulsion, it is possible to use one of those described above or an emulsion produced by adding 20 g. of 4-monotertiary butyl pyrocatechol, 5.5 g. of cyclopentanone bisulphite, 200 g. of crystallized sodium acetate, cc. of glycerol and stabilizers and other conventional emulsion additives to one litre of a silver halide emulsion.

Positive: As the transfer layer there is used either a metal or plastic foil or a coated paper to which the emulsion-binding agent adheres poorly in the moist condition. Suitable for this purpose is a paper coated with cellulose acetobutyrate or acetyl cellulose. The paper is prepared by treating the support with a 2 to 4% solution of the aforementioned substances in acetone. The transfer from the negative to the positive is carried out as described in the foregoing examples.

The positive is then dyed with an aqueous dyestuff solution as in Example 2 and transferred to a metal or rubber roller which has been prepared beforehand with an adhesive substance. For the adhesive preparation, it is possible to use waxes and greases or mixtures thereof or even thickened linseed oil or plastic solutions of similar character. A condition for this preparation is, however, that it be a good adhesive substance for the emulsion particles swelled by the dyestuff solution, but does not hold or soil either the positive support or the paper to be printed. The layer of this preparation applied to the roller should not be made too thick, since otherwise the transferred emulsion particles are displaced by the roller pressure. If a paper moistened with water is now brought into contact with this roller, the non-laterally reversed dyestuff image of the original is obtained on the paper.

The emulsion particles can also be dyed on the roller, and it is then only necessary for a moistening of the positive to precede the printing on to the roller.

Moreover, if the roller with positive impression is dyed beforehand, it can also be moistened with water or else an aqueous dyestutf solution and then it can be brought into contact with the paper to be printed.

EXAMPLE 4 Positive for Ofiset Printing Negative: Any of the emulsions described in Example 1 to 3 can be used as negative emulsion.

Positive: Any metal, paper or plastic foil suitable for the offset process and commercially available can be used as transfer layer. The processing is carried out as in Example 1, except that a plate or foil suitable for the offset process is used instead of the transfer layer described in the said example and the non-laterally reversed positive of the original is obtained on the plate or foil. This plate is washed for a short time in a 3% aqueous solution of zirconium oxychloride, whereupon it is rinsed and is then ready for printing. It is also sufiicient to coat the plate with the zirconium salt solution and then quickly wash it off.

We claim:

1. An image reproduction process comprising the steps of exposing to an object to be reproduced a layer of gelatin emulsion of silver halide containing a developer that hardens the gelatin, said gelatin being impermeable to alcoholic dyestuif solutions but being coated on a support which is permeable to alcoholic dyestufi solutions, placing said exposed emulsion in contact with a transfer support, heating the resulting assembly to a temperature of about -150 C. in the presence of compounds splitting ofi moisture in an amount sufficient to cause the emulsion to have from about 8 to 12% moisture by weight and to cause the exposed areas of the emulsion to be reduced and the gelatin in these areas to be hardened without adhering to the transfer support, while the unexposed areas of the emulsion are stripped from the emulsion support and become adhered to the transfer support, separating the transfer support with the adhering emulsion areas from the exposed emulsion so that a negative relief image is obtained in the exposed emulsion and a positive relief image on the transfer support, dyeing the back of the negative with an alcoholic dyestutf solution, and then transferring the image on the negative to another carrier held in contact with the front of the negative, this being effected by the penetration of the dyestuif through the emulsion-free areas of the negative on to said carrier.

2. A process according to claim 1 wherein the silver halide emulsion is held on a paper support by means of a thin intermidate coating of a film forming substance which is swellable in alcohol and thus permeable to dyestufl".

References Cited in the file of this patent UNITED STATES PATENTS 1,954,325 Martinez Apr. 10, 1934 2,012,526 Whitmore Aug. 27, 1935 2,292,311 Wirtz Aug. 4, 1942 2,458,376 Henn Jan. 4, 1949 2,596,756 Yutzy et a1. Mar. 13, 1952 2,675,313 Yutzy et a1. Apr. 13, 1954 2,704,712 Jackson Mar. 22, 1955 2,716,059 Yutzy et a1. Aug. 23, 1955 2,747,999 Yutzy et al May 29, 1956 2,903,964 Taylor Sept. 15, 1959 2,942,975 Erde June 28, 1960 2,971,840 Haydn et a1. Feb. 14, 1961 FOREIGN PATENTS 392,938 Great Britain May 26, 1933 399,269 Great Britain Oct. 5, 1933 

1. AN IMAGE REPRODUCTION PROCESS COMPRISING THE STEPS OF EXPOSING TO AN OBJECT TO BE REPRODUCED A LAYER OF GELATIN EMULSION OF SILVER HALIDE CONTAINING A DEVELOPER THAT HARDENS THE GELATIN, SAID GELATIN BEING IMPERMEABLE TO ALCOHOLIC DYESTUFF SOLUTIONS BUT BEING COATED ON A SUPPORT WHICH IS PERMEABLE TO ALCOHOLIC DYESTUFF SOLUTIONS, PLACING SAID EXPOSED EMULSION IN CONTACT WITH A TRANSFER SUPPORT, HEATING THE RESULTING ASSEMBLY TO A TEMPERATURE OF ABOUT 80-150* C. IN THE PRESENCE OF COMPOUNDS SPLITTING OFF MOISTURE IN AN AMOUNT SUFFICIENT TO CAUSE THE EMULSION TO HAVE FROM ABOUT 8 TO 12% MOISTURE BY WEIGHT AND TO CAUSE THE EXPOSED AREAS OF THE EMULSION TO BE REDUCED AND THE GELATIN IN THESE AREAS OF THE EMULSION TO WITHOUT ADHERING TO THE TRANSFER SUPPORT, WHILE THE UNEXPOSED AREAS OF THE EMULSION ARE STRIPPED FROM THE EMULSION SUPPORT AND BECOME ADHERED TO THE TRANSFER SUPPORT, SEPARATING THE TRANSFER SUPPORT WITH THE ADHERING EMULSION AREAS FROM THE EXPOSED EMULSION SO THAT A NEGATIVE RELIEF IMAGE IS OBTAINED IN THE EXPOSED EMULSION AND A POSITIVE RELIEF IMAGE ON THE TRANSFER SUPPORT, DYEING THE BACK OF THE NEGATIVE WITH AN ALCOHOLIC DYESTUFF SOLUTION, AND THEN TRANSFERRING THE IMAGE ON THE NEGATIVE TO ANOTHER CARRIER HELD IN CONTACT WITH THE FRONT OF THE NEGATIVE, THIS BEING EFFECTED BY THE PENETRATION OF THE DYESTUFF THROUGH THE EMULSION-FREE AREAS OF THE NEGATIVE ON TO SAID CARRIER. 